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In this work, TiO 2 nanocrystalline thin films were obtained through evaporating Ti films by electron beam deposition (EBD) followed by thermal treatment. The results show that after annealing at 300, 400 and 450 °C for 8 h, the obtained TiO 2 thin films have nanoparticle and nanorod structures of 15–30 nm diameter and 100–300 nm length. At 750 °C for 8 h, the rutile phase was formed. The incorporation of cadmium sulfide (CdS) into TiO 2 nanoparticle thin films was investigated. A CdS thin film was vacuum deposited onto the pre-deposited TiO 2 film by a thermal evaporation technique. The obtained TiO 2 and TiO 2/CdS nanocomposite films were characterized by x-ray diffraction (XRD) and a field emission scanning electron microscope (FE-SEM). The TiO 2/CdS composite film was used in a photo-electrochemical (PEC) cell as a working electrode and in a platinum electrode as a counter electrode. The electrolyte solution contains 1 M KCl and 0.1 M Na 2 S. The results show that the cell with the TiO 2/CdS composite film electrode has significantly improved photoelectric capability in comparison with that of pure TiO 2 thin films, and the best thickness of the CdS thin film deposited on the ITO/TiO 2 substrates is 70–140 nm.

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Tin dioxide (SnO2) has recently been recognized as an excellent electron transport layer (ETL) for perovskite solar cells (PSCs) due to its advantageous properties, such as its high electron mobility, suitable energy band alignment, simple low-temperature process, and good chemical stability. In this work, nitrogen-doped graphene quantum dots (N-GQDs) were prepared using a hydrothermal method and then used to fabricate N-GQD:SnO2 nanocomposite ultrathin films. N-GQD:SnO2 nanocomposite ultrathin films were investigated and applied as electron transport layers in planar PSCs. The presence of N-GQDs with an average size of 6.2 nm in the nanocomposite improved its morphology and reduced surface defects. The excitation–emission contour map indicated that the N-GQDs exhibited a remarkably enhanced light-harvesting capability due to the possibility of absorbing UV light and producing emissions in the visible range. The quenching of photoluminescence spectra showed that the N-GQDs in nanocomposite ultrathin films improved electron extraction and reduced charge recombination. As a result, the power conversion efficiency (PCE) of our planar PSCs fabricated with the optimized N-GQD:SnO2 nanocomposite electron transport layer was improved by 20.4% over pristine SnO2-based devices.